The deployment of cryptography in sensor networks is a challenging task, given the limited computational power and the resource-constrained
nature of the sensoring devices. This paper presents the implementation of
elliptic curve cryptography in the MICAz Mote, a popular sensor platform.
We present optimization techniques for arithmetic in binary fields, including
squaring, multiplication and modular reduction at two different security levels.
Our implementation of field multiplication and modular reduction algorithms
focuses on the reduction of memory accesses and appears as the fastest result
for this platform. Finite field arithmetic was implemented in C and Assembly
and elliptic curve arithmetic was implemented in Koblitz and generic binary
curves. We illustrate the performance of our implementation with timings for
key agreement and digital signature protocols. In particular, a key agreement
can be computed in 0.40 seconds and a digital signature can be computed and
verified in 1 second at the 163-bit security level. Our results strongly indicate
that binary curves are the most efficient alternative for the implementation of
elliptic curve cryptography in this platform.